The relationship of QRS morphology and mechanical dyssynchrony to long-term outcome following cardiac resynchronization therapy.

Aims: Because benefits of cardiac resynchronization therapy (CRT) appear to be less favourable in non-left bundle branch block (LBBB) patients, this prospective longitudinal study tested the hypothesis that QRS morphology and echocardiographic mechanical dyssynchrony were associated with long-term outcome after CRT.
Methods and Results: Two-hundred and seventy-eight consecutive New York Heart Association class III and IV CRT patients with QRS ≥120 ms and ejection fraction ≤35% were studied. The pre-specified primary endpoint was death, heart transplant, or left ventricular assist device over 4 years. Dyssynchrony assessed before CRT included interventricular mechanical delay (IVMD) and speckle-tracking radial strain using pre-specified cut-offs for each. Of 254 with baseline quantitative echocardiographic data available, 128 had LBBB, 81 had intraventricular conduction delay (IVCD), and 45 had right bundle branch block (RBBB). Radial dyssynchrony was observed in 85% of the patients with LBBB, 59% with IVCD*, and 40% with RBBB* (*P < 0.01 vs. LBBB). Of 248 (98%) with follow-up, LBBB patients had a significantly more favourable long-term survival than non-LBBB patients. However, non-LBBB patients with dyssynchrony had a more favourable event-free survival than those without dyssynchrony: radial dyssynchrony hazard ratio 2.6, 95% confidence interval (CI) 1.47-4.53 (P = 0.0008) and IVMD hazard ratio 4.9, 95% CI 2.60-9.16 (P = 0.0007). Right bundle branch block patients who lacked dyssynchrony had the least favourable outcome.
Conclusion: Non-LBBB patients with dyssynchrony had a more favourable long-term survival than non-LBBB patients who lacked dyssynchrony. Mechanical dyssynchrony and QRS morphology are associated with outcome following CRT.